The present invention relates to identification and localization of objects tagged with passive microwave responsive devices. More particularly, a system architecture facilitating identification of passive microwaves tags in room sized spaces is described.
Improved information dissemination and organization for individuals or organizations is enhanced with a stable and reliable mechanism for tracking and locating multiple tagged objects in conventional room or office sized areas. Tagged objects can be assembled, manipulated, and maintained to create, alter, preserve, share, or coordinate information. For example, wall mounted pin boards or magnetic boards can be used by an individual or group to transiently or semi-permanently display documents, calendars, task schedules, phone number lists, project proposals, informational flyers, meeting announcements, photographs, maps, or any other desired information. In some cases, small physical artifacts such as keys or magnetic icons can even be attached to the surface.
Advantageously, such tagged documents or objects allow for ready manipulation of documents or artifacts through addition, removal, replacement, reordering, or stacking. For example, a team""s project schedule might be represented on a wall mounted pin board by pin attached task cards arranged in a timeline format. Such task cards can be easily altered or physically moved with respect to a displayed timeline as people leave a project, schedules slip, or any other problems develop. Unfortunately, this easy alteration of information by individuals or group members presents its own set of problems. Attached task cards can be inappropriately removed, misplaced, or obscured. Obscuration is a particular problem for still or video camera based tracking systems, infrared or laser systems, or acoustic based systems. Obscuration of such tags can make recording state of the pin board at a given time for electronic archival or tracking purposes effectively impossible.
Accordingly, the present invention automatically or semiautomatically integrates a computational system and a passive microwave based spatial tracking system that does not require an unobscured line of sight for operation. Tagged documents or objects (e.g. a pin board with spatially differentiated pin mounted task cards, each card having an affixed identity tag detectable by microwave tracking systems) can be made part of a computational system by sensing the identity, position, and contents of the component artifacts. In effect, each task card has its content and position stored in a database, with movement of a particular task card automatically resulting in update of the database to record the new position of that task card. Tagged objects are typically documents, but may be physical icons, or other small physical artifacts attachable by magnets, pins, adhesives, frictional forces, or other conventional attachment mechanisms. Informational content of at least some of the plurality of tagged components can be directly determined by transfer/reading of information (which may be either an address to an electronic document, or the document information itself) from a passive microwave tag, or determined by position based associations maintained by a computer based microwave tracking system.
In preferred embodiments, the microwave tracking system provides a database with information necessary for constructing a series of time dependent snapshots of position and informational content. This database is updateable to reflect changes in position and informational content, while still retaining a time/action addressable record of state changes of the plurality of microwave tagged objects. This allows, for example, a user to digitally replay changes in a microwave tagged object collection, or determine the state of microwave tagged objects a day, a week, or a month earlier.
As will be appreciated by those skilled in the art, certain microwave tags may not be merely associated with electronic data (e.g. an electronically available text document or picture), but may actually xe2x80x9coperatexe2x80x9d on other tagged objects to define data relationships between tagged objects. Data can be altered, combined, erased, saved, augmented, transferred, or otherwise modified through provision of various digital services associated with xe2x80x9coperator iconsxe2x80x9d. In operation, a tagged object having associated electronic data is physically associated with an operator icon, causing modification of that associated electronic data in response to physical association of the operator icon with a tagged object. For example, consider a first tagged document and a second tagged object representing a user. An operator icon symbolically configured as a pointing arrow can be positioned to point from the first tagged object to the second tagged object. This association causes the system to electronically mail the first document to the user. Reversal of the arrow so that the arrow points from the user to the document can result in modification of document properties so that the user is linked to the document and informed of any updates, changes, or alterations to the document.
As will be appreciated, the foregoing scenarios require precise spatial discrimination of tagged objects, reliable transfer of data from the tag to the tracking system, and in some cases may even require transmission of data to the tag (for resetting identification numbers or adding information). Accordingly, for the purposes of the present invention microwave based systems (generally, but not exclusively operating in a frequency range of about 1 GHz to 30 GHz) for identification, spatial localization, and optional data transmission to tags are preferred over other known localization systems (e.g. camera based optical or acoustic). A microwave base station for tracking microwave tags allows for high speed scanning of a room with a narrow beam (providing angular localization), or use of multiple base stations for triangulation (providing three dimensional spatial triangulation). Passive microwave tags consume very little power since they do not directly emit radiation, but act by backscattering, or selectively modifying reflection of the microwave beam. The strong distance dependence (1/r4) of the microwave beam enhances separation between multiple base stations operating in a room, and permits pinpoint location of tags responding with encoded identification or other information. As will be appreciated, to help further distinguish tags, in certain embodiments mechanical or electrical phase shift techniques may be employed to reduce problems with half wave null positions for microwave tags relative to microwave base stations.
As will be understood, microwave tags can be purely passive, with passive backscattering information from resonant structures being predefined during tag construction. For example, a backscattered wave from a stub will be modulated (changing with respect to the directed microwave beam) in both amplitude and phase as the electrical length of the stub is varied. Such modulation can be accomplished by changing the voltage on a varactor diode connected to the stub, and generally requires very little power, since only a small back biased diode is continuously driven. A small CMOS circuit powered by a small lithium battery is therefore capable of continuously generating an identifiable signal in response to a directed microwave beam for a duration of several years.
Alternatively, more advanced microwave tags can be provided with additional analog or digital circuits for self modification (e.g. in response to tagged attached sensor or user input), or for modification in response to microwave base station requests. In certain embodiments of the present invention, active circuits in the tags can modifiable in response to both user input at the tag site (including voice data), and from the base station, permitting two way voice or other communications at very low power using precise microwave beam positioning to provide space-division multiplexing. This would be useful, for example, in connecting to an IP telephony system through a mobile phone handset equipped with suitable two way microwave tags. Using the present invention, a two way communication system with a low power mobile handset having a video type detector with baseband processing for the receiver and the self modifiable passive circuit for backscattering a microwave beam from the base station can be constructed. Such a system would have a very low receiver power consumption, essentially no transmit power consumption, and because of the spatially localized nature of the base station microwave beam, would not require complex time-division multiplexing or dynamic allocation schemes (e.g. MACA) for supporting multiple handsets in a room without interference.
Additional functions, objects, advantages, and features of the present invention will become apparent from consideration of the following description and drawings of preferred embodiments.